After several years, I am on my second BMW tank bag. The first one's zipper gave up the ghost and its window turned yellow from UV exposure.

Does anyone have a good idea how to keep the BMW tank bag window from yellowing?

All I can think of is only use it in sunshine when actually riding and turn it upside down and put it on the seat when stopping in sunlight. The latter is easy to do because it snaps on and off so quickly. But these are less than wondrous solutions.

I also thought of sewing up a fabric tank bag cover with elastic around the edges so I can just put it on and off easily. But I haven't hauled out the sewing machine to make that. I may do that yet if someone doesn't have better solution to stop the UV.

Because of BMW's snap-on-and-off mounting system, I am not interested in getting a different tank bag, so that is not a solution for me.